This proposal seeks to compare the mechanical characteristics of the systemic venous system in certain experimental animals in relation to their application to man. Through our current studies of the effect of chemoreceptor stimulation we have also begun to investigate those humoral factors which govern the control of both venous return and ventilation and those factors, such as blood flow itself, which interrelate to these two important cardiovascular-pulmonary functions. We also seek to investigate the influence that changes in venous mechanical parameters have on transvascular movement of fluid between interstitial and vascular compartments and how this shift affects venous return. In anesthetized animals, various types of cardiopulmonary bypass have been devised to 1) separate the systemic circulation from the pulmonary circulation, and 2) to separate venous return into splanchnic and non-splanchnic vascular beds. These preparations allow us to control blood flows, blood pressure, and blood gases while determining blood volume shifts, venous compliance, arterial and venous resistances and ventilation. These experiments will allow us to identify how much of the information concerning the control of venous return in the dog can be transferred to other species and will contribute to our understanding of the linkage between intra- and extravascular fluid compartments. By means of these experiments we will also begin to integrate several large bodies of physiologic information, i.e., principles related to circulatory mechanics and those principles governing the control of ventilation and the hydraulic conductivity through the capillary wall.